(1) Field of the Invention
The present invention relates generally to acoustic sonar systems and, more specifically, to methods for evaluating, comparing, and selecting sonar system configurations and sonar sensors.
(2) Description of the Prior Art
Variable depth sonar arrays are routinely tested at a variety of depths to determine their system performance. Sonar performance may vary greatly with depth because of changes in factors that affect the sensors such as temperature and depth. Typically, near the surface, temperature is the primary consideration. As the depth increases, then pressure has a greater influence on performance as temperature becomes more uniform. At intermediate depths, ducts form which can trap transmitted acoustic waves and allow them to propagate for large distances. Moreover, if the transmitting and receiving sensors in a sonar system are at widely varying depths, then acoustic boundaries caused by pressure and temperature may interfere with sound wave reception. An acoustic sonar system may also vary with respect to the organization or sensors within the array.
More specifically, sensor and system performance is determined by performing a variety of tests at various ranges and depths. The purpose of the tests is to determine the maximum range of reception for a given depth. Often the maximum range values are averaged together to provide a value which represents the combined sensor performance. This may lead to an incorrect evaluation because the sensor may have an exceptionally large range value within a duct which will overshadow lesser values at other depths.
As an example for evaluating a sonar system in a surface layer environment, a sonar system that maintains both transmitting and receiving sensor arrays in the surface layer may normally achieve a relatively large detection range for a target that also appears in the surface layer but may produce comparatively small detection ranges for targets that are situated below the surface duct. When the result of all target depths are combined in a simple average or referenced to a statistical measurement such as standard deviations, the outcome may be skewed by the shallow event. Standard deviations give a value indicating the closeness of the data to the average and so standard deviation is meaningless without a reference to the average value. Accordingly, whenever standard deviation is provided, the average is provided.
Use of standard deviation techniques also results in difficulty of comparison. For instance, one system may average fifteen kiloyards (fifteen thousand yards) with a standard deviation of three kiloyards. The next system may average sixteen and one-half kiloyards with a standard deviation of four kiloyards. With this type of comparison, there is no clear answer as to which is the better system. Moreover, these results are difficult to plot due to extra dimensions as compared with a single performance rating.
The result is that prior art methods for comparing sonar sensors and sonar sensor systems may lead to an unrealistic or inaccurate appraisal of the system""s detection capability against targets at all water depths and may cause selection of a less desirable sonar system.
Prior art patents that relate to this topic include the following:
U.S. Pat. No. 5,734,591, issued Mar. 31, 1998, to John C. Yundt, (hereinafter, Yundt ""591) discloses a method for analyzing biochemical samples or human bodily fluids which operates over at least two ranges. The method of Yundt ""591 comprises obtaining a first set of test results relating to the biochemical samples from the testing device over at least two ranges, and calculating from the first set of test results an individual range mean for each of the at least two ranges. The method also includes obtaining a second set of test results relating to the biochemical samples from a group of testing devices that operate over the at least two ranges, calculating from the second set of test results a group range mean and a group range standard deviation for each of the at least two ranges, and calculating standard deviation indexes for the testing device from the individual range means, the group range means and group range standard deviations. The method further comprises forming generally parallel spaced apart data range axes, each relating to a range of operation of the testing device, to facilitate analysis of the performance of the testing device over each range of operation, wherein the respective positions of the data range axes in relation to one another are scaled based on the values of the operating ranges, and then plotting all of the standard deviation indexes in relation to the data range axes in such a way that, analysis of the performance of the testing device over the at least two operating ranges is provided in a single graphic display.
U.S. Pat. No. 5,541,854, issued Jul. 30, 1996 to John C. Yundt, discloses a method and graph for analyzing the performance of a testing device that operates over at least two ranges related to the above U.S. Pat. No. 5,734,591, to the same inventor.
U.S. Pat. No. 5,828,567, issued Oct. 27, 1998, to Eryurek et al., discloses a transmitter in a process control system including a resistance sensor sensing a process variable and providing a sensor output. Sensor monitoring circuitry coupled to the sensor provides a secondary signal related to the sensor. Analog-to-digital conversion circuitry coupled to the sensor output and the sensor monitoring circuitry provides a digitized sensor output and a digitized secondary signal. Output circuitry coupled to a process control loop transmits a residual life estimate related to residual life of the sensor. A memory stores a set of expected results related to the secondary signal and to the sensor. Diagnostic circuitry provides the residual life estimate as a function of the expected results stored in a memory, the digitized sensor output and the digitized secondary signal.
U.S. Pat. No. 4,675,147, issued Jun. 23, 1987, to Schaefer et al, discloses the real time actual and reference values of parameters pertinent to the key safety concerns of a pressurized water reactor nuclear power plant which are used to generate an integrated graphic display representative of the plant safety status. This display is in the form of a polygon with the distances of the vertices from a common origin determined by the actual value of the selected parameters normalized such that the polygon is regular whenever the actual value of each parameter equals its reference value despite changes in the reference value with operating conditions, and is an irregular polygon which visually indicates deviations from normal otherwise. The values of parameters represented in analog form are dynamically scaled between the reference value and high and low limits which are displayed as tic marks at fixed distances along spokes radiating from the common origin and passing through the vertices. Multiple, related binary signals are displayed on a single spoke by drawing the associated vertice at the reference value when none of the represented conditions exist and at the high limit when any such condition is detected. A regular polygon fixed at the reference values aids the operator in detecting small deviations from normal and in gauging the magnitude of the deviation. One set of parameters is selected for generating the display when the plant is at power and a second set reflecting wide range readings is used the remainder of the time such as following a reactor trip. If the quality of the status, reference or limit signals associated with a particular vertex is xe2x80x9cbadxe2x80x9d, the sides of the polygon emanating from that vertex are not drawn to appraise the operator of this condition.
In summary, while the prior art shows various methods for making comparisons, the above disclosed prior art does not show a suitable method for comparing sonar sensors or sonar sensor systems. Consequently, there remains a need for a system that provides a single performance rating that accounts for both the average and deviation from the average for performance at different target depths which may be plotted for different sender/receiver depth configurations. Those skilled in the art will appreciate the present invention that addresses the above and other problems.
Accordingly, it is an object of the present invention to provide an improved method for comparing acoustic sensors and acoustic sensor systems.
It is yet another object of the present invention to provide a method of comparison of acoustic sensors and acoustic systems that provides a single performance rating that takes into effect the depth sensitive nature of performance of the acoustic sensors and acoustic sensor systems.
These and other objects, features, and advantages of the present invention will become apparent from the drawings, the descriptions given herein, and the appended claims.
A method is provided for evaluating and/or selecting a sonar system wherein the sonar system comprises at least one sender and at least one receiver. The method includes such steps as positioning the sender and the receiver at a plurality of sensor depths wherein tests are performed for each of the plurality of sensor depths. For instance in one test, the sender may be located at a one hundred foot depth and the receiver at a three hundred foot depth. In a subsequent test, both the sender and receiver may be at a two hundred foot depth. Different sonar system configurations which may comprise only one sender/receiver or may comprise sensor arrays or different sonar systems can be evaluated as discussed below.
For each of the plurality of sensor depths or sonar system configurations, a target may be positioned at a plurality of target depths. For each of the plurality of target depths, a detection range is determined for the sonar system, e.g., twenty kiloyards at one target depth, eighteen kiloyards at another target depth, and so on. An average detection range is determined.
Moreover, a scaling factor related to a ratio of the dynamic range to the maximum range is produced. A dynamic range sensitivity weighting term is selected. The value of the dynamic range sensitivity weighting is typically but not necessarily selected to be between zero and one. Preferably, the range weighting term is selected to be no greater than the smallest value of the inverse of the scaling factor.
For each of the plurality of sensor depths, a performance rating is produced from the average detection range, the dynamic range, the maximum detection range, the minimum detection range, and the dynamic range sensitivity weighting term. More specifically, the minimum detection range may be subtracted with respect to the average detection range to provide a first factor. The dynamic range sensitivity weighting term may be multiplied with respect to the first factor to obtain a second factor. The scaling factor may be multiplied with respect to the second factor to obtain a dynamic range factor. Then the dynamic range factor may be subtracted with respect to the average detection range to provide a performance rating.
As noted above, the performance rating is preferably determined with respect to each of the plurality of sensor depths. In one preferred embodiment, the performance rating may be plotted for each of the plurality of sensor depths.
With respect to comparison and selecting purposes, it is desirable to utilize a constant value for the range weighting term for each of the plurality of sensor depths and/or for each sonar system or sonar system components to be tested.